1. Field of the Invention
This invention relates to a process for purifying hydrochloric acid produced from an alkali chloride and sulfuric acid. More particularly, it relates to a process for purifying hydrochloric acid produced from an alkali chloride and sulfuric acid, by treating it with an inert gas or a mixed gas of an inert gas with oxygen to remove volatile impurities included therein.
2. Description of the Prior Art
A process in which hydrogen chloride is generated by reacting an alkali chloride with sulfuric acid and caused to be absorbed in water to provide hydrochloric acid (this process will hereinafter be referred to as conversion process), does not consume a large amount of electric power and, unlike an alkali chloride-electrolysis process, hydrogen chloride, not chlorine, can be directly obtained and a useful alkali sulfate can be simultaneously obtained. Thus, in this regard, this process is one of the techniques which might be looked over again at the present time to meet the demand of energy saving.
However, the hydrochloric acid produced according to the conversion process contains Br.sub.2 and other coloring materials, as volatile impurities formed by the reaction of an alkali chloride with sulfuric acid, and in order to remove effectively such volatile impure coloring materials (which will be hereinafter referred to as volatile impurities, etc.), such a treatment as rectification has been necessary to obtain hydrochloric acid useful for chemical industries.
In view of the above-mentioned status of hydrochloric acid produced according to the conversion process (which will hereinafter be referred to as conversion process-hydrochloric acid), we have been studying a process for removing the slightest amounts of volatile impurities, etc. which are formed by the conversion reaction and which are included in the conversion process-hydrochloric acid to thereby purify the acid. As a result of our earnest study, it has been found that such removal and purification can be effected at a single stroke without necessity of rectification, by treating the conversion process-hydrochloric acid with an inert gas or a mixed gas of oxygen with an inert gas. When a mixed gas of oxygen with an inert gas is used, if Br.sub.2 and other coloring materials are oxidized in the liquid, it is anticipated that coloring materials such as bromic acid and other coloring materials which are hardly distillable, form in the conversion process-hydrochloric acid and remain as impurities. By such a way of thinking the present invention is considered to relate to an unpredictably useful technique.
As evident from the foregoing description, an object of the present invention is to provide a process for purifying a conversion process-hydrochloric acid which does not require any special purifying step such as rectification (though it is doubtful whether or not Br.sub.2 and the like can be removed sufficiently by rectification). Another object of the present invention is to provide a conversion process-hydrochloric acid purified according to the above-mentioned process.